Re: [PATCH v3 2/2] rpmsg: glink: Update cdev add/del API in rpmsg_ctrldev_release_device()

[Stephen Boyd]

The subject is a little confusing. Maybe it should be "Use
cdev_device_{add,del}() instead of open coding".

Quoting Sujit Kautkar (2021-11-02 16:51:51)
> Replace cdev add/del APIs with cdev_device_add/cdev_device_del to avoid
> below kernel warning. This correctly takes a reference to the parent
> device so the parent will not get released until all references to the
> cdev are released.
>
> | ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x7c
> | WARNING: CPU: 7 PID: 19892 at lib/debugobjects.c:488 debug_print_object+0x13c/0x1b0
> | CPU: 7 PID: 19892 Comm: kworker/7:4 Tainted: G        W         5.4.147-lockdep #1
> | ==================================================================
> | Hardware name: Google CoachZ (rev1 - 2) with LTE (DT)
> | Workqueue: events kobject_delayed_cleanup
> | pstate: 60c00009 (nZCv daif +PAN +UAO)
> | pc : debug_print_object+0x13c/0x1b0
> | lr : debug_print_object+0x13c/0x1b0
> | sp : ffffff83b2ec7970
> | x29: ffffff83b2ec7970 x28: dfffffd000000000
> | x27: ffffff83d674f000 x26: dfffffd000000000
> | x25: ffffffd06b8fa660 x24: dfffffd000000000
> | x23: 0000000000000000 x22: ffffffd06b7c5108
> | x21: ffffffd06d597860 x20: ffffffd06e2c21c0
> | x19: ffffffd06d5974c0 x18: 000000000001dad8
> | x17: 0000000000000000 x16: dfffffd000000000
> | BUG: KASAN: use-after-free in qcom_glink_rpdev_release+0x54/0x70
> | x15: ffffffffffffffff x14: 79616c6564203a74
> | x13: 0000000000000000 x12: 0000000000000080
> | Write of size 8 at addr ffffff83d95768d0 by task kworker/3:1/150
> | x11: 0000000000000001 x10: 0000000000000000
> | x9 : fc9e8edec0ad0300 x8 : fc9e8edec0ad0300
> |
> | x7 : 0000000000000000 x6 : 0000000000000000
> | x5 : 0000000000000080 x4 : 0000000000000000
> | CPU: 3 PID: 150 Comm: kworker/3:1 Tainted: G        W         5.4.147-lockdep #1
> | x3 : ffffffd06c149574 x2 : ffffff83f77f7498
> | x1 : ffffffd06d596f60 x0 : 0000000000000061
> | Hardware name: Google CoachZ (rev1 - 2) with LTE (DT)
> | Call trace:
> |  debug_print_object+0x13c/0x1b0
> | Workqueue: events kobject_delayed_cleanup
> |  __debug_check_no_obj_freed+0x25c/0x3c0
> |  debug_check_no_obj_freed+0x18/0x20
> | Call trace:
> |  slab_free_freelist_hook+0xb4/0x1bc
> |  kfree+0xe8/0x2d8
> |  dump_backtrace+0x0/0x27c
> |  rpmsg_ctrldev_release_device+0x78/0xb8
> |  device_release+0x68/0x14c
> |  show_stack+0x20/0x2c
> |  kobject_cleanup+0x12c/0x298
> |  kobject_delayed_cleanup+0x10/0x18
> |  dump_stack+0xe0/0x19c
> |  process_one_work+0x578/0x92c
> |  worker_thread+0x804/0xcf8
> |  print_address_description+0x3c/0x4a8
> |  kthread+0x2a8/0x314
> |  ret_from_fork+0x10/0x18
> |  __kasan_report+0x100/0x124
>
> Signed-off-by: Sujit Kautkar <sujitka@xxxxxxxxxxxx>
> ---

Reviewed-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>